[Haskell-cafe] Trapped by the Monads

Bill Wood william.wood3 at comcast.net
Tue Sep 20 14:51:26 EDT 2005

   . . .
> What struck me was this bit of code:
> assemblyLine w = (return w) >>= makeChopsticks >>= polishChopsticks >>= wrapChopsticks
> Interestingly, this looks like Forth (!), where you put a value on the 
> stack, and successive operations fiddle with the stack as a series of 
> transformations. Not that I know Forth, you understand. Hmm, so Haskell 
> can be a concatenative language if you want it to be.

Some time ago I had occasion to model a special-purpose machine in SML,
and the potential users wanted a programmatic interface that looked like
an assembly language for the machine.  I modeled the instructions as
curried functions with the machine state as the last parameter and
return value, and defined a "reverse compose" function -- (f >> g) x ===
g (f x).  This allowed me to write programs with op codes and parameters
running down the page, just like real assembler (I tabbed over to place
the ">>" so they kinda hung out in the comment area so as not to spoil
the illusion).  It was a quick 'n dirty hack that turned out to be
pretty slick.

 -- Bill Wood
    bill.wood at acm.org

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